Special Printing 15 Cent. 1875?

@pisti
Thanks for the much improved images. Much better control of the lighting. The discoloration I mentioned earlier is not so evident and I am not so sure it was from a cancellation as from a bit of sulfide toning of the ink in the image.


sinclair wrote:




In view of the much improved image I tend to agree that this is a 152, but I am curious about the association of this guide arrow with plate #20. What reference/study are you using for that? Anything published? This is interesting to me.

rogdcam wrote:



Yes it does, and it is not the property to which reference should have been made. The type of lighting should have been called "transillumination" and the feature being examined is "opacity." More than the intensity of the light is at issue in this kind of study inasmuch as the focus of interest is the structure of the paper and not the illumination. At the level presented so far this is only a qualitative study.

The guide arrows on Plate 20 and Plate 31 are different enough from each other to easily tell the two apart. The angle of the arrow is somewhat flat on Plate 31 and quite a bit steeper on Plate 20. I couldn't find a top guide arrow for Plate 20 on powersearch to see if it's the same as the bottom but I suspect that it is. Even if we did not have the guide arrow, there is absolutely no hint of a secret mark.